The present invention relates to an electric vehicle, and more particularly, to a battery temperature management method of an electric vehicle capable of decreasing charge time and obtaining a maximum charge amount (Ah) during fast charging by active control of the temperature of the battery.
Generally, the battery that provides the main power to an electric vehicle is one of the most important components that determines the quality of the vehicle. Thus, a typical electric vehicle is equipped with a battery management system (xe2x80x9cBMSxe2x80x9d) that manages all of the states of the battery by monitoring battery states. The BMS also provides information to an upper controller on the charging/discharging current limitation values of the battery based on the temperature of the battery, the surrounding temperature, and the charging state, thereby optimizing use of the electric vehicle.
The temperature of the battery is increased by chemical reactions, and this causes the ratio of charging capacity to rating capacity of the battery to be reduced. Also, when the battery is charged at an improper temperature, the battery can be damaged due to over-charging, and the vehicle""s mileage can be reduced due to low-capacity charging. Further, at low temperatures, fast charging cannot be performed since the charge power may be especially low from reduced charging capacity.
Thus, in an electric vehicle, it is very important to maintain the battery at an optimal temperature to be able to charge the battery to its maximum amount, and to control the temperature of the battery so that charging at high power levels is possible.
FIG. 1 shows a conventional battery temperature management method. When the battery is being charged in a conventional electric vehicle, the BMS determines whether a detected temperature is higher than 38 degrees (S601). When the temperature of the battery is determined to be lower than 38 degrees, the current state is maintained, and when the temperature is determined to be higher than 38 degrees, a battery-cooling fan is turned on in a first stage to perform cooling of the battery (S602). When the first stage of battery cooling is enabled, the BMS determines whether the temperature of the battery is higher than 46 degrees (S603).
If the temperature of the battery is determined to be higher than 46 degrees, the second stage of the cooling fan is enabled to accelerate cooling of the battery (S604). When the temperature is determined to be lower than 46 degrees, the BMS next determines whether the battery temperature is higher than 36 degrees (S605). If the battery temperature is determined to be higher than 36 degrees, driving of the cooling fan is maintained in the first stage, and when the battery temperature is determined to be lower than 36 degrees, the cooling fan is stopped (S606).
When the cooling fan is operated in the second stage to cool the battery, the BMS determines whether the battery temperature is higher than 44 degrees (S607). If the battery temperature is determined to be higher than 44 degrees, the procedure returns to step S603, and when the battery temperature is determined to be lower than 44 degrees, the second stage operation of the cooling fan is turned off (S608) and the procedure returns to step S601.
The aforementioned battery temperature management method, which is summarized in FIG. 2, has several disadvantages. For example, the cooling fan is only used when the temperature of the battery is increased, and the cooling fan is not operated until the temperature of the battery increases to a predetermined temperature, so fast charging is not ordinarily performed. In addition, since the battery is maximally cooled to an external temperature, the battery can be damaged and vehicle mileage can be reduced due to undercharging or overcharging in a hot area or in a cold area. In particular, in a cold area, this method may limit the maximum charging power.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.
In a preferred embodiment of the present invention, the method for managing temperature of a battery of an electric vehicle comprises: determining whether a battery charge mode is a fast-charging mode based on state information of the battery; determining whether a value of a state of charge (SOC) is lower than a predetermined SOC value, when the battery charge mode is the fast-charging mode; detecting a temperature of the battery and comparing the detected temperature with a reference value for each stage therewith, when the value of SOC is lower than the predetermined SOC value; and regulating the temperature of the battery by controlling power output of a heater in response to a result of comparing the battery temperature with the reference value for each stage.
The method for managing temperature of a battery also comprises: detecting a temperature of the battery and comparing a difference between the detected temperature of the battery and a predetermined value with the reference temperature for each stage, when the current SOC value is determined to be less than the reference SOC value; and regulating the temperature of the battery by driving a cooling fan in response to a result of comparing the difference between the detected temperature of the battery and the predetermined value with the reference value for each stage at a final state of charging.
Preferably, the reference SOC value is set in a range of approximately 80xcx9c90%. Also, preferably, the temperature of the battery for beginning to drive a cooling fan of the temperature control system is set at approximately 40 degrees. Further, it is preferable that the power output of the heater for increasing the temperature of the battery is increased as the temperature of the battery is decreased. The preferable range of the temperature of the battery for adjusting the power output of the heater is set in intervals of approximately 10 degrees.
It is also preferable that the driving strength of the cooling fan according to the temperature of the battery at the final state of charging is adjusted for each stage. The preferable range of the temperature of the battery for driving control of the cooling fan at the final state of charging is set in intervals of approximately 10 degrees. Preferably, the adjustment of the driving of the cooling fan and the power output of the heater of the temperature control system is varied according to characteristics of the battery.
In another preferred embodiment of the present invention, a method for managing temperature of a battery of a electric vehicle comprises: determining whether a value of a state of charge of a battery is less than a predetermined value; regulating temperature of the battery such that the temperature of the battery approaches a temperature for a maximum charge power of the battery, if the value of the state of charge of the battery is less than the predetermined value; and regulating temperature of the battery such that the temperature of the battery approaches a temperature for a maximum charge amount of the battery, if the value of the state of charge of the battery is greater than the predetermined value.
Preferably, if the value of the state of charge of the battery is less than the predetermined value, the step of regulating temperature of the battery comprises: determining whether the battery temperature is higher than a first predetermined temperature; determining whether the battery temperature is higher than a second predetermined temperature, if the battery temperature is higher than the first predetermined temperature; and decreasing the battery temperature such that the battery temperature approaches the temperature for the maximum charge power of the battery by cooling the battery, if the battery temperature is higher than the second predetermined temperature.
It is also preferable that, if the value of the state of charge of the battery is less than the predetermined value, the step of regulating temperature of the battery further comprises: increasing the battery temperature such that the battery temperature approaches the temperature for the maximum charge power by heating the battery, if the battery temperature is not higher than the first predetermined temperature.
It is further preferable that if the if the value of the state of charge of the battery is greater than the predetermined value, the step of regulating temperature of the battery comprises: determining whether a difference between the battery temperature and a predetermined temperature is less than a predetermined value; and decreasing the battery temperature such that the battery temperature approaches the temperature for the maximum charge amount in response to the difference between the battery temperature and the predetermined temperature, if the difference is not less than the predetermined value.
In yet another preferred embodiment of the present invention, a battery temperature management system comprises a battery temperature control apparatus and a battery control unit. The battery temperature control apparatus includes a battery heating unit and a battery cooling unit.
The battery control unit is coupled to the battery temperature control apparatus to control temperature of the battery, and it is programmed to perform a battery temperature control method comprising: determining whether a value of a state of charge of the battery is less than a predetermined value; regulating temperature of the battery such that the temperature of the battery approaches a temperature for a maximum charge power of the battery, if the value of the state of charge of the battery is less than the predetermined value; and regulating temperature of the battery such that the temperature of the battery approaches a temperature for a maximum charge amount of the battery, if the value of the state of charge of the battery is not less than the predetermined value.
Another preferred embodiment of the present invention is a method for managing temperature of a battery of an electric vehicle comprising: determining whether a value of a state of charge (SOC) is lower than a predetermined SOC value; and detecting a temperature of the battery. When the value of the SOC is lower than the predetermined SOC value, the method comprises comparing the detected temperature with a plurality of reference values, each reference value corresponding to a boundary of a plurality of battery temperature states, and each battery temperature state corresponding to a stage of a battery heater; and regulating the temperature of the battery by controlling the battery heater in accordance with the stage of the battery heater corresponding to a result of comparing the detected temperature of the battery with the reference value.
Also, when the value of the SOC is greater than the predetermined SOC value, the method comprises: comparing a difference between the detected temperature of the battery and a predetermined value with a plurality of reference temperatures, each reference temperature corresponding to a boundary of a plurality of battery temperature states, and each battery temperature state corresponding to a stage of a battery cooling fan; and regulating the temperature of the battery by driving the cooling fan in accordance with the stage of the cooling fan corresponding to a result of comparing the difference between the detected temperature of the battery and the predetermined value with the reference value.